Abrasive articles, in general, include a plurality of abrasive particles and a binder. Examples of abrasive articles include bonded abrasive articles (such as grinding wheels), coated abrasive articles, nonwoven abrasive articles, to name a few. Coated abrasive products typically have a backing substrate, abrasive particles, and a binder system which operates to hold the abrasive particles to the backing. For example, in a typical coated abrasive product, the backing is first coated with a layer of binder, commonly referred to as a "make" coat, and then the abrasive particles are applied to the binder coating. As so applied, the abrasive particles optimally are at least partially embedded in the make coat. The resulting binder/abrasive particle layer is then generally solidified or set (such as by a series of drying or curing ovens) sufficient to retain the adhesion of abrasive particles to the backing. After precuring or setting the make coat, a second layer of binder, commonly referred to as a "size coat," is applied over the surface of the make coat and abrasive particles, and, upon setting, it further supports the particles and enhances the anchorage of the particles to the backing. Optionally, a "supersize" coat, which may contain grinding aids, can be applied over the precured size coat. In any event, once the size coat and supersize coat, if used, has been cured, the resulting coated abrasive product can be converted into a variety of convenient forms such as sheets, rolls, belts, and discs.
There exists a subclass of fillers, typically referred to as grinding aids. Grinding aids can be especially effective in abrading stainless steel, exotic metal alloys, titanium, metals slow to oxidize, and so forth. In some instances, a coated abrasive product containing a grinding aid in the binder can abrade significantly more stainless steel than a corresponding coated abrasive product in which the binder is devoid of a grinding aid. It is believed that one function of a grinding aid is to prevent metal capping by rapidly contaminating the freshly formed metal surface. Grinding aids are normally incorporated into the binder(s) of the abrasive article. Examples of common grinding aids include sodium aluminum hexafluoride (i.e., cryolite), sodium chloride, potassium tetrafluoroborate (KBF.sub.4), iron pyrite, polyvinyl chloride, and polyvinylidene chloride.
Titanium alloys, in particular, such as those designed for aerospace applications and other applications where high strength to weight ratios are desirable, are extremely difficult to grind, even with coated abrasive articles including conventional grinding aids. Poor grinding efficiency of such materials may be alleviated somewhat by use of certain externally supplied grinding fluids, such as coolants or lubricants. These grinding aids typically flood the grinding interface between the abrasive article and the workpiece surface. Materials used as grinding aids or lubricants for titanium typically include soluble cutting oils such as highly chlorinated cutting oils. For example, I. S. Hong et al. describe solutions including inorganic tripotassium phosphate and an acid (H.sub.3 PO.sub.4) or an acid salt (NaH.sub.2 PO.sub.4) as a lubricant in titanium grinding with a coated abrasive article. Hong, I. S. et al., "Coated Abrasive Machining of Titanium Alloys With Inorganic Phosphate Solutions," Trans. ASLE, 14 (1971), pages 8-11. Other known lubricants typically include an inorganic salt, such as NaNO.sub.2, KNO.sub.2, Na.sub.3 PO.sub.4, and K.sub.3 PO.sub.4, as described by Cadwell et al., "Grinding a Titanium Alloy With Coated Abrasives," ASME Paper 58-SA-44, June, 1958. In International Publication No. WO 97/14535 Gagliardi et al., an abrasive article is described which contains tripotassium phosphate.
U.S. Pat. No. 4,770,671 (Monroe et al.) describes adding various types of grinding aids onto the surface of alpha-alumina-based ceramic abrasive grits in coated abrasive articles. In one example, Monroe et al. describe including K.sub.2 HPO.sub.4 in a supersize coat of an amine-curable epoxy resin.
Attempts in the past have been directed toward new grinding aids to improve the efficiency of abrasive articles to abrade metal workpieces, such as titanium metal. Although these attempts have been somewhat successful, the industry continues to search for improvements in abrasive articles, the use of which results in a more efficient abrading of metal.